<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div>
        <p>点击下面的按钮，只要 i 小于 5 就一直循环代码块。</p>
        <button onclick="myFunction()">点击这里</button>
        <p id="demo"></p>
        <script>
            function myFunction() {
                var x = "", i = 0;
                while (i < 5) {
                    x = x + "该数字为 " + i + "<br>";
                    i++;
                }
                document.getElementById("demo").innerHTML = x;
            }
        </script>
    </div>
    <hr>
    <div>
        <p>点击下面的按钮，只要 i 小于 5 就一直循环代码块。</p>
        <button onclick="wasddas()">点击这里</button>
        <p id="wasddas"></p>
        <script>
            function wasddas() {
                var x = "", i = 0;
                do {
                    x = x + "该数字为 " + i + "<br>";
                    i++;
                }
                while (i < 5)
                document.getElementById("wasddas").innerHTML = x;
            }
        </script>
    </div>
</body>

</html>